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In April 1999, the Environmental Health Investigations Branch of the California Department of
Health Services, under a cooperative agreement with the Agency for Toxic Substances and
Disease Registry (ATSDR), released a health consultation entitled "Lawrence Livermore
National Laboratory Plutonium Contamination in Big Trees Park" [1]. That public health
consultation reported the results of an analysis of the potential health effects of plutonium-associated radiological doses that might be received by individuals visiting the park. The analysis
indicated that health effects were unlikely and that the potential for plutonium-associated
radiological doses in the park was not a matter of public health concern.

The question of how the plutonium (Pu1) reached the park was not completely addressed in that
health consultation. ATSDR and California Department of Health Services (CDHS) made three
specific recommendations regarding the need for additional sampling in Big Trees Park. These
recommendations as published were as follows:

We recommend further sampling of Big Trees Park and the Arroyo Seco Creek sediments
to determine the vertical and horizontal extent of the Pu 239 contamination.

We recommend further evaluation of the distribution of contaminated sludge throughout
the Livermore Valley, and other areas. This would include assessing the different avenues
for gathering information on where sludge may have been distributed, and if locations are
identified that may have received contaminated sludge, assessing the feasibility of various
approaches to characterize the potential plutonium in those areas.

We recommend that potential contaminant releases from sewer line ruptures be
investigated in future health consultations focusing on sediments in the Livermore Valley
or LLNL discharges to the sanitary sewer system.

ATSDR is preparing this public health consultation to address the following issues: (1) overall
quality of the data collected during the 1998 Big Trees Park sampling event; (2) evaluation of the
possible pathways by which plutonium reached the park; (3) evaluation of metals contaminants
in Big Trees Park; and (4) if additional consideration should be given for an area-wide sampling
for plutonium in residential soils.

ATSDR held a series of public meetings in the city of Livermore in 1997 and 1998. One outcome
of these meetings was that the regulatory agencies composed of the U.S. Environmental
Protection Agency (EPA), the U.S. Department of Energy (DOE), and the California Department
of Health Services Radiological Health Branch agreed that additional sampling in Big Trees Park
was warranted. DOE and the Lawrence Livermore National Laboratory (LLNL), with regulatory
oversight, developed a new sampling plan. This sampling plan was released for public comment
and was finalized in October 1998 [2]. This plan included a split sampling plan in which
approximately 10% of the samples collected would be supplied to ATSDR for independent
analysis [3].

As stated in the sampling plan, the purpose of the 1998 round of sampling was to describe
methodologies, analytical procedures, and related tasks to determine how the plutonium
identified in the previous public health consultation could have reached the park. Environmental
samples were to be collected for pathway analysis. Soil samples were to be collected at various
locations and depths in Big Trees Park. Major sampling locations included (1) samples selected
by use of a grid to determine the possibility of an air dispersion pathway; (2) the current Arroyo
Seco channel and the old channel before the realignment of the creek to determine the possibility
of a water pathway resulting from releases of plutonium from the LLNL via sewer line breaks or
by overland flow from the southeast quadrant of the laboratory; and (3) sampling in and areas
around ornamental trees to determine the potential for a soil pathway resulting from the use of
contaminated sewage sludge as a soil amendment. Other sampling areas included the Big Trees
Park eastern extension; the playground of the Arroyo Seco Elementary School; and a disked area
chosen on the basis of a request by a community member. The disk area was sampled to
determine whether the dust and dirt in the area presented the possibility of a possible inhalation
and ingestion pathway. While a detailed discussion of the rationale associated with these
locations is beyond the scope of this consultation, the information is available in the 1998
Sampling Plan [2].

Previous Sampling Events

The results of the first sampling of Big Trees Park were released in 1994 when the EPA National
Air and Radiation Environmental Laboratory was doing confirmatory surveys of plutonium
contamination in the southeast quadrant of LLNL [4]. Big Trees Park and two additional city
parks in Livermore were chosen to represent areas considered background. Sampling results
indicated that plutonium levels might be elevated in the surface soils of these parks. In 1995, in
response to the discovery of plutonium in the soil samples from Big Trees Park, LLNL resampled
the soil at Big Trees Park for verification purposes [5]. Details of these sampling events can be
found in the previous public health consultation [1] and two other documents [4, 5].

Each of the previous sampling efforts had different data quality objectives. Because of this and
several other reasons, the data between these sets should not have been analyzed as a combined
group. ATSDR's reasons for this belief include, but are not limited to, a lack of available
interlaboratory quality control and assurance information from independent laboratories;
variations in the methodologies used for the analyses; issues concerning lower limits of
detection; and the precision and accuracy for the intercomparison of data sets. These factors have
been discussed at several public meetings, and the California Department of Health Services,
ATSDR, and the regulatory agencies involved have also discussed these issues through a series
of correspondence. Additional discussion of the previous data sets is not warranted and is
beyond the scope of this consultation.

Data Quality, Quality Control, and Quality Assurance Activities

For the 1998 sampling of Big Trees Park, the issues of data quality were addressed through a
more rigorous oversight by EPA and the California Department of Health Services; public
participation via a comment period; a split sampling plan among LLNL, EPA, and ATSDR; and
regulatory analysis of the split sampling data by EPA. ATSDR was involved in this process in
the following three ways: (1) ATSDR served as a central collection point for public comments;
(2) ATSDR arranged for an independent laboratory analysis of approximately 10% of the
collected samples; and (3) ATSDR participated in the data quality review.

The data quality team was established with representatives from the Lawrence Livermore
National Laboratory, the Radiological Health Branch of the California Department of Health
Services, and from DOE, EPA, and ATSDR. Members of the team were selected on the basis of
their knowledge of radiation chemistry, radiological measurement protocols, and familiarity with
radiation measurement instrumentation. Identical data packages including results, quality control
samples, protocols and analysis procedures were supplied and reviewed by this team. Discussions
on the methods for the team's review were discussed in the DOE offices in Oakland, California,
before the samples were collected. Present for these technical discussions were representatives
from ATSDR, DOE, EPA, LLNL, and both the Radiological Health Branch and the
Environmental Health Investigations Branch of the California Department of Health Services.
Additional technical deliberations and discussions of data validation issues were conducted
through conference telephone calls or by electronic mail.

The EPA Quality Assurance office in San Francisco also requested a review of the quality control
and quality assurance issues by its Office of Radiation and Indoor Air in Montgomery, Alabama,
and the Indoor Environments National Laboratory in Las Vegas, Nevada. The latter organization
also reviewed the analytical methods and the quality control procedures of the participating
laboratories, and evaluated the results with respect to the samples collected according to the split
sampling plan. This evaluation concluded that, overall, the data among the laboratories were in
close agreement and stated that "most of the data is useable without qualification" [6].

Statistical considerations for radiological data analysis

Typically, results from the analysis of radioactive samples are expressed as a 3-number set that
includes the measured result, an indication of the uncertainty in the measurement, and the
minimum detectable activity. Therefore, many statistical considerations must be taken into account
during the evaluation of these samples, especially those samples at or near values considered
background values. These considerations include method of sample collection and preservation,
the methods of analysis, and laboratory quality control and assurance that the samples are handled
identically. These issues all contribute to the general term "error," which is best defined as
uncertainty in the measurements. Furthermore, the instruments used to measure the radioactivity
also contribute to the uncertainty, with the uncertainty of the measurement denoted as the 2 sigma
error (2). The 2 sigma error represents a 95% confidence interval that the reported value is correct
with only a 5% chance that the "true" number is outside the range in the given interval. For
example, 10 plus or minus 3 (10 ± 3) means that the measured value is 10 with an uncertainty of 3.
This is interpreted as the possibility of the true number being between 7 and 13. Occasionally, the 2
sigma error is larger than the measured value, for example, 10 ± 15. With the uncertainty factor
this great, the sample should be considered a nondetect or zero.

When analyzing radiological samples with concentrations that approach either the lowest level that
can be detected by the instrumentation or the levels associated with background, the 2 sigma error
increases dramatically. Therefore, finding 2 sigma values approaching 50% or more of the
measured value is common in these situations and these data could be considered not significantly
different from background; that is, a nondetection.

For this consultation, ATSDR analyzed the data using the following guidelines which were
established by ATSDR before the start of the evaluation:

Does the laboratory-derived value exceed the minimum detectable activity (MDA)? If the value
is less than the MDA, then the sample measurement is not significant and no additional
evaluation is needed.

Does the laboratory-derived value exceed the reporting limit as outlined in the sampling plan?
If the sample is above the reporting limit, continue with the evaluation.

Is the measured laboratory-derived measurement greater than the MDA but less than the
reporting level? If so, continue with the evaluation.

Is the 2 interval less than the laboratory-derived measurement and what percentage does it
represent? If the 2 interval is less than 25% of the laboratory reported value, consider the
measurement a valid measurement. If the 2 interval is more than 25%, attempt to evaluate
using other methods--such as duplicate samples.